The present invention relates to electric motor driven centrifugal fluid pumps and particularly to pumps of the sort that have no rotating axle or bearings that penetrate a wall of the pump housing and so the housing is completely sealed against any leakage of the fluid that is pumped and there is no requirement of seals against leakage of the fluid at any moving or rotating part of the pump.
Heretofore, magnetically driven centrifugal pumps that are completely sealed up and have no drive shaft or bearing opening through any wall of the housing of the pump have been provided. Such pumps are often specified where, for any number of reasons, no fluid leakage from the pump can be tolerated and the motor power is 1/8 horsepower (HP) or less. For example: the fluid may be very contaminating; or it may be poisonous or radioactive; or it may simply be a cooling fluid in a closed system that cannot tolerate any leaks. For any of these reasons, magnetically driven pumps have been provided in which the drive from the electric motor to the rotor of the pump is by magnetic coupling through a wall of the pump housing and so there need not be any drive shaft or bearing that penetrate the wall of the pump housing and the performance is below 3 gallons per minute (gpm) at a pressure head of 30 to 50 feet (1/8 HP or less).
The fluid input of such a pump is along the axis and may be into an axial input chamber at the front inside of the housing and from that chamber into rotating radial passages that are partly defined by the impellers attached to the rotor. The fluid is trapped in these rotating radial passages between the impellers and the immediately adjacent front inside wall of the housing and is compelled to flow radially into a peripheral annular output chamber within the housing. The pressure of fluid at the input chamber is the input pressure and the pressure at the peripheral annular chamber is the output pressure and the effect of the rotation is to increase the output pressure over the input pressure even while there is a continuous flow of fluid into the input and out of the output. As volume flow increases the pressure head decreases (maximum pressure head is achieved at zero flow).
Such a pump is described in U.S. Pat. No. 4,927,336, issued May 22, 1990, entitled "Magnetically Driven Pump", to Ferdinand Lustwerk, the inventor herein. That patent describes a radial magnetically driven pump in which the pump rotor axle is supported within then sealed pump housing at only the driven end thereof; it is cantilevered from that end inside of the housing. The cantilevered pump rotor axle is preferred so that the front face of the rotor that carries the impellers has no axle between it and the opposite wall (front inside wall) of the housing as this allows a fluid input along the axis of rotation directly into the center of the impeller face of the rotor.
The impellers define radial fluid passages leading from the axial center of the front of the housing to the periphery of the housing. An axial input fluid port is at the front of the housing and an output fluid port is at the periphery of the housing. The rotor drive includes several radially oriented magnets outside of the housing magnetically coupled through the walls of the housing with the rotor magnets inside the housing. In operation, rotation of the external drive rotates the rotor causing fluid to flow from the input to the output increasing the pressure of the fluid at the output with respect to the pressure of the fluid at the input.
For electric motor driven centrifugal pumps over 1/8 HP, that are usually required to deliver more than 25 inch-ounces of torque at 5,000 revolutions per minute (RPM), the magnetic coupling has, for the above reasons, been found to be inadequate. However, for such pumps there is still the problem that the fluid pumped may be very contaminating; or it may be poisonous or radioactive; or it. may simply be a cooling fluid in a closed system that cannot tolerate any leaks. It is an object of the present invention to provide an improved electric motor driven centrifugal fluid pump wherein the fluid is an oil, the motor is an oil submersible electric motor and a sealed housing contains the fluid, the motor and the pump.
With a fluid submersible motor contained within the sealed housing with the pump as in the present invention, there is an advantage in cooling the motor by providing means for compelling the fluid to flow through parts of the motor and carry heat therefrom so that the motor can be operated at higher power without overheating. For example, a 1/2 HP submersible motor driving a 2 to 3 gpm pump at 30 to 50 foot high pressure head, may heat the fluid that is pumped to 280.degree. F., which is excessive. Hence, it is another object of the present invention to provide such a pump and electric drive motor in an assembly contained within a sealed housing wherein means are provided for compelling some fluid flow around the electric motor to cool the motor while the pump is driven in operation.
With a submersible motor and centrifugal pump contained within a sealed housing and the pump fluid input at low pressure is axial at the front of the pump and the pump output at high pressure is at the periphery of the pump, the fluid pressure around the motor and between the motor and the pump rotor is at the output high pressure level. Thus, the pump rotor has a greater pressure on one side than the other and exerts a thrust load or pull on the motor drive shaft which is resisted at the motor bearings. For example, a 1/2 HP submersible motor driving a 2 to 3 gpm pump at 30 to 50 foot high pressure head may experience a 27 pound thrust load on the motor bearings. It is another object of the present invention to provide such a pump and electric drive motor in an assembly contained within a sealed housing wherein means are provided for compelling some fluid flow around the electric motor to reduce the static pressure on the pump rotor and so reduce the thrust load on the motor bearings.
The static pressure in a fluid is the pressure perpendicular to the direction of the fluid flow velocity. The total pressure is the static pressure plus the velocity pressure. Where there is no flow velocity, there is no velocity pressure and static pressure and total pressure are equal.